United States Department of Homeland Security Secretary Kirstjen Nielsen speaks to the local news media against the backdrop of the border wall, Wednesday, Dec 13, 2017, in Hidalgo, Texas. The new head of the U.S. Department of Homeland Security says she hopes construction on a border wall will begin soon. (Joel Martinez/The Monitor via AP) less

United States Department of Homeland Security Secretary Kirstjen Nielsen speaks to the local news media against the backdrop of the border wall, Wednesday, Dec 13, 2017, in Hidalgo, Texas. The new head of the ... more

Photo: Joel Martinez, MBI / Associated Press

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Secretary of Homeland Security Kirstjen Nielsen listens as Attorney General Jeff Sessions speaks at a news conference in Baltimore, Tuesday, Dec. 12, 2017, to announce efforts to combat the MS-13 street gang with law enforcement and immigration actions. (AP Photo/Patrick Semansky) less

Even as fewer immigrants were caught by U.S. Border Patrol agents during the 2017 fiscal year, ending in September, a recent uptick in apprehensions and a spike in attacks on border agents underscore the need for more wall, according to Nielsen.

A week after her Senate confirmation, Nielsen visited the Texas border, calling attention to the death of Rogelio Martinez, a border agent killed last month in West Texas, and the 786 attacks on border agents during the 2017 fiscal year, up from 403 attacks in 2016.

The FBI has searched the vehicle of two brothers, one of whom is in the country illegally, after an informant said they were involved in Martinez’s killing, but local law enforcement officials have said Martinez could have been hit by a vehicle or died in a fall and officials have not said an assault took place.

“The department continues to mourn the death of Border Patrol agent Martinez, who recently gave his life in the line of duty,” Nielsen said. “While we await the results of the FBI investigation, what we do know is this year saw a horrifying increase in assaults on Border Patrol agents.”

Nielsen, who replaced White House chief of staff John F. Kelly, said the Trump administration hopes to begin wall construction soon, but noted that quite a few issues have not yet been sorted out.

Earlier this week, the National Butterfly Center filed a lawsuit against DHS calling for the government to comply with federally mandated environmental assessments. A section of wall is planned to slice through the 100-acre nature and wildlife sanctuary.

The Trump administration has already waived environmental laws to replace a small stretch of border wall in California, and it expected to do the same in the Rio Grande Valley, where it plans to build 28 miles of new levee wall and 32 miles of new border wall.

The agency is testing and evaluating prototypes for Trump's border wall outside of San Diego.

“I think the idea of any assessment … is to share the results with the community and then have a discussion about how to proceed,” Nielsen said in response to questions about the butterfly center lawsuit.

In a short statement on plans to reform the nation’s immigration system, Nielsen said lax standards have led to an explosion in dubious asylum claims, causing a backlog in the immigration court system and crowded detention centers.

“Border security is both stopping the illegal entrants, and also expeditiously removing those who come into our country illegally,” Nielsen said.

Nielsen was in Austin on Tuesday where she praised Texas’ controversial law banning so-called sanctuary cities, and urged other states to follow Texas’ example. The administration is further urging Congress to deny certain grants and funding to sanctuary jurisdictions, she said.

“I have one message for those thinking of coming here illegally,” Nielsen said with her back to the border fence. “You’re time is up, we will no longer stand for this.”